Method and device for receiving a multimedia broadcast multicast service in a mobile communication system

ABSTRACT

The present invention relates to a method and device for receiving a multimedia broadcast multicast service (MBMS) in a mobile communication system. The method for receiving the MBMS of a terminal in the mobile communication system according to an embodiment of the present invention is characterized in that it includes: determining whether service area ID (SAI) information on a serving cell is broadcast during the MBMS; receiving the SAI information on the serving cell when it is determined that the SAI information is broadcast; determining, by using the received SAI information of the serving cell, whether an SAI of the MBMS matches the SAI of the serving cell; and changing the cell reselection priority of the frequency of the serving cell to the highest priority if it is determined that the SAI of the MBMS matches the SAI of the serving cell. According to the present invention, it is possible to efficiently receive MBMS services by enabling a terminal to select a proper frequency or cell when an MBMS service of interest starts.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of prior application Ser. No.14/347,854, filed on Mar. 27, 2014, which is a U.S. National Stageapplication under 35 U.S.C. §371 of an International application filedon Oct. 10, 2012 and assigned application number PCT/KR2012/008208,which claimed the benefit of U.S. Provisional applications filed on Oct.10, 2011, Oct. 27, 2011, Nov. 14, 2011, Nov. 23, 2011, Feb. 6, 2012, andFeb. 17, 2012 in the U.S. Patent and Trademark Office and assigned Ser.Nos. 61/545,363, 61/552,114, 61/559,674, 61/563,345, 61/595,646, and61/600,179 respectively, and a Korean patent application filed on Oct.10, 2012 in the Korean Intellectual Property Office and assigned Serialnumber 10-2012-0112390, the entire disclosure of each of which is herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to a method and apparatus for receivingMultimedia Broadcast Multicast Service (MBMS) in a mobile communicationsystem.

BACKGROUND

Mobile communication systems developed to provide the subscribers withvoice communication services on the move. With the rapid advance oftechnologies, the mobile communication systems have evolved to providehigh speed data communication services beyond the voice communicationservices.

Recently, as one of the next generation mobile communication system,Long Term Evolution (LTE) is on the standardization by the 3rdGeneration Partnership Project (3GPP). LTE is a technology designed toprovide high speed packet-based communication of up to 100 Mbps and hasbeen standardized almost currently.

In order to provide broadcast service in the mobile communicationsystem, Multimedia Broadcast Multicast Service (MBMS) has beenintroduced. MBMS is a technology for broadcast of multimedia contentsefficiently and allows the terminals to identify the MBMS frequency toreceive the MBMS signals without report to the base station.

In order to achieve this, there is a need of a method and procedure forallowing the terminal to identify the frequency or cell providing theservice which the user is interested.

SUMMARY

The present invent has been conceived to solve the above problem andaims to provide a method and procedure for a terminal to identify thefrequency or cell providing the user-interested service.

In accordance with an aspect of the present invention, a MultimediaBroadcast Multicast Service (MBMS) reception method of a terminal in amobile communication system includes determining whether a Service AreaIdentifier (SAI) of a serving cell is broadcast in progress of the MBMS,receiving, when the SAI of the serving cell is broadcast, the SAI of theserving cell, determining whether the SAI of the MBMS match the SAI ofthe serving cell, and changing, when the SAI of the MBMS matches the SAIof the serving cell, a cell reselection priority of a frequency of theserving cell to a highest priority.

In accordance with another aspect of the present invention, a MultimediaBroadcast Multicast Service (MBMS) reception apparatus of a terminal ina mobile communication system includes a controller which controlsdetermining whether a Service Area Identifier (SAI) of a serving cell isbroadcast in progress of the MBMS, receiving, when the SAI of theserving cell is broadcast, the SAI of the serving cell, determiningwhether the SAI of the MBMS match the SAI of the serving cell, andchanging, when the SAI of the MBMS matches the SAI of the serving cell,a cell reselection priority of a frequency of the serving cell to ahighest priority.

The method and apparatus for receiving MBMS of the present inventionmakes it possible for the terminal to select the frequency or cellproviding the interested service when MBMS starts so as to receive theMBMS efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the architecture of an LTE system towhich the present invention is applied.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

FIG. 3 is a diagram illustrating Multimedia Broadcast Multicast service(MBMS).

FIG. 4 is a flowchart illustrating a method of adjusting the cellreselection priority of the MBMS frequency in consideration of theinterested MBMS service start time and Service Area ID (SAI) accordingto an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a method for determining whether theUE attempts bearer reconfiguration after unicast bearer has beenreleased due to the cell congestion according to an embodiment of thepresent invention.

FIG. 6 is a flowchart illustrating a method for a UE non-interested inreceiving MBMS to adjust the cell reselection priority of a cellproviding MBMS according to an embodiment of the present invention.

FIG. 7 is a flowchart illustrating a method for the UE which isinterested in receiving MBMS to determine whether to transmit accessnotification message according to an embodiment of the presentinvention.

FIG. 8 is a diagram illustrating carrier aggregation.

FIG. 9 is a flowchart illustrating a method for the UE configured with aplurality of serving cells to perform random access according to anembodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Detailed description of well-known functions and structures incorporatedherein may be omitted to avoid obscuring the subject matter of thepresent invention. Exemplary embodiments of the present invention aredescribed with reference to the accompanying drawings in detail. Priorto the explanation of the present invention, LTE system and carrieraggregation is described briefly.

FIG. 1 is a diagram illustrating the architecture of an LTE system towhich the present invention is applied.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135connects to an external network via eNBs 105, 110, 115, and 120 and theS-GW 130

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to the legacy nodeBs of the UMTS system. The eNBs 105, 110, 115, and 120 allow the UE toestablish a radio link and are responsible for complicated functions ascompared to the legacy node B. In the LTE system, all the user trafficincluding real time services such as Voice over Internet Protocol (VoIP)are provided through a shared channel and thus there is a need of adevice which is located in the eNB to schedule data based on the stateinformation such as UE buffer conditions, power headroom state, andchannel state. Typically, one eNB controls a plurality of cells. Inorder to secure the data rate of up to 100 Mbps, the LTE system adoptsOrthogonal Frequency Division Multiplexing (OFDM) as a radio accesstechnology. Also, the LTE system adopts Adaptive Modulation and Coding(AMC) to determine the modulation scheme and channel coding rate inadaptation to the channel condition of the UE. The S-GW 130 is an entityto provide data bearers so as to establish and release data bearersunder the control of the MME 125. MME 125 is responsible for variouscontrol functions and connected to a plurality of eNBs 105, 110, 115,and 120.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical(PHY) 220 and 225. The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. The MAC215 and 230 is responsible for establishing connection to a plurality ofRLC entities so as to multiplex the RLC PDUs into MAC PDUs anddemultiplex the MAC PDUs into RLC PDUs. The PHY 220 and 225 performschannel coding on the MAC PDU and modulates the MAC PDU into OFDMsymbols to transmit over radio channel or performs demodulating andchannel-decoding on the received OFDM symbols and delivers the decodeddata to the higher layer.

A description is made of MBMS briefly hereinafter.

The MBMS server 305 generates MBMS data to the eNBs 310, 315, 320, 325,and 330 participated in MBMS transmission. The eNBs store the datareceived from the MBMS server and transmit the data at a predeterminedtime. Since the same data are transmitted simultaneously, this gives aneffect of amplifying the signal strength, and the UEs receiving the samesignal from multiple eNBs can experience the high received signalquality as compared to the case of receiving the signal from one eNB. Inorder for the eNBs to transmit the same signal, there should be a fewassumptions as follows.

First, the eNBs have to receive the same data. Secondly, the eNBs haveto generate same data from the same data. Finally, the same data have tobe transmitted on the same transmission resource simultaneously.

The neighbor eNBs transmit the same MBMS data, and some MBMS servicesare likely to be provided in a certain area. The area where a certainMBMS service is provided (or a set of cell or frequencies) is referredto as MBMS Service Area.

It is preferred that the UE in the idle mode camps on a frequencyproviding the MBMS service. This is because the UE camped on a non-MBMSfrequency has to monitor the paging channel of the serving frequencywhile receiving the MBMS service on the MBMS frequency.

In order for the idle mode UE which is interested in or receiving theMBMS service currently to operate on the frequency providing MBMS(hereinafter, referred to as MBMS frequency), the MBMS interested UE hasa capability of adjusting the cell reselection priority of the MBMSfrequency. The UE operation concerning this is depicted in FIG. 4.

FIG. 4 is a flowchart illustrating a method of adjusting the cellreselection priority of the MBMS frequency in consideration of theinterested MBMS service start time and Service Area ID (SAI) accordingto an embodiment of the present invention.

The UE acquires the service guide information including variousinformations concerning MBMS and checks the information on the UEinterested MBMS service at step 405. The service guide information isprovided by MBMS service provider, MBMS server, and MBMS serviceoperator and may include the following informations per MBMS service.

-   -   Service Area ID (SAI): Identifier indicating the area where the        corresponding MBMS service is provided. The SAI may be provided        in the system information of the cell and, if the SAI of the        UE-interested MBMS service matches the SAI broadcast in the        system information, the UE determines that the corresponding        MBMS service is provided in the corresponding cell (or on the        corresponding frequency).    -   Frequency: Frequency on which the corresponding MBMS service is        provided.    -   Service start time: Time when the service starts.

Afterward, the UE determines whether the interested MBMS service is inprogress at step 410. If the interested MBMS service is in progress,i.e. if the current time is later than the service start time, theprocedure goes to step 420. If the interested MBMS service is notstarted yet, i.e. if the current time is earlier than the service starttime, the procedure goes to step 415. At step 415, the UE waits for thestart time of the interested MBMS service, and the procedure goes tostep 420 at or right before the service start time.

The UE determines whether the current serving cell broadcasts SAIinformation at step 420. If no SAI information is broadcast, theprocedure goes to step 425 and, otherwise, step 430.

The SAI information is provided in a System Information Block (SIB)which may include the SAIs of neighboring frequencies as well as thecurrent cell. Typically, SAI is provided by frequency and thus theserving cell SAI has the same meaning of the serving frequency SAI. Forexample, if there is a certain serving cell (frequency f1) and theneighboring frequencies f2, f3, and f4 on which f1 and f2 are used forMBMS, the SAIs of the serving cell and f2 may be broadcast in a certainSIB.

Assuming that the SIB carrying the SAI information is SIB X, the UEchecks the SIB X of the serving cell to determine whether the SAIinformation is broadcast. If it is determined that the SIB X of theserving cell carries the SAI information, the procedure goes to step430. If it is determine that the SIB X of the serving cell carries noSAI information or if no SIB X is broadcast, the procedure goes to step425.

The reason why the network provides the SAI information is to indicatewhether the UE-interested MBMS service is provided in the current area.For example, if the UE-interested MBMS service is provided in theCapital area and if the UE out of the Capital area may not receive theSAI of the interested MBMS service in the current area. Accordingly, theUE determines whether the interested MBMS service is provided in thecurrent area based on the presence/absence of the SAI of the interestedMBMS service and, if not the MBMS service area, suspends additionaloperation for receiving the MBMS service, e.g. adjustment of the cellreselection priority.

Depending on the Release of eNB, the SAI information may be provided ornot. If the eNB is a REL-10 or earlier release eNB, this means that theSAI-related operation is not performed and thus the eNB does notbroadcast SAI information. That is, SIB x is not broadcast. If the eNBis REL-11 or later release eNB, it broadcasts SAI information. That is,if the serving cell does not provide SAI information, it is impossibleto determine whether the MBMS service is provided in the current areabased on SAI. At this time, if the MBMS service frequency exists in thecurrent area, the UE assumes that the MBMS service is provided in thecorresponding area and performs follow-up operation.

If it is determined that the interested MBMS service frequency ispresent at step 425, the UE adjusts the cell reselection priority of thefrequency to the highest value at step 429. If the interested MBMSservice is not provided in a predetermined time since the cell of theinterested MBMS service frequency is selected, the UE may recover thecell reselection priority to the original value. If it is determinedthat the interested MBMS service frequency is not present at step 425,the UE waits until the serving cell changes or the system information ischanged or reacquired at step 427.

If the interested MBMS service frequency is present, this means that theserving frequency or neighboring frequency is the interested MBMSservice frequency. The neighbor frequency is indicated in the systeminformation of the serving cell.

The cell reselection priority is the priority allocated per frequency,and the UE selects the cell operating on the frequency having the highpriority with priority. For example, if the channel quality of thefrequency having the highest priority is better than the a predeterminedthreshold, the cell operating on the frequency having the highestpriority is likely to be selected although the channel quality of thecell operating on another frequency is better. The cell reselectionpriority may be provided in the system information or sent from the eNBto the UE through a dedicated RRC message in releasing the RRCconnection.

If it is determined that the ASI information is broadcast at step 420,the procedure goes to step 430. At step 430, the UE determines whetherthe SAI information includes the SAI matching the interested MBMS SAI.If the interested MBMS SAI is present, the procedure goes to step 435and, otherwise if the interested MBMS SAI is absent, step 437.

At step 435, the UE adjusts the cell reselection priority of thefrequency corresponding to the SAI matching the MBMS SAI (hereinafter,referred to interested SAI) to the highest value. If the SAI of theserving cell is the interested SAI, the interested SAI frequency is theserving frequency and, otherwise if the SAI of the neighbor frequency isthe interested SAI, the interested SAI frequency is the neighborfrequency. If the interested MBMS service is not provided in apredetermined time after reselecting the cell of the interested SAIfrequency, the UE recovers the cell reselection priority to the originalvalue. The UE waits until the serving cell is changed or the systeminformation is changed or reacquired at step 437.

FIG. 5 is a flowchart illustrating a method for determining whether theUE attempts bearer reconfiguration after unicast bearer has beenreleased due to the cell congestion according to an embodiment of thepresent invention.

The idle mode UE may transition to the connected mode for a certainreason. After transitioning to the connected mode to receive the MBMSservice, the UE has to provide the eNB with the information necessaryfor the MBMS service. In the present invention, the followinginformations (hereinafter, MBMS informations) are provided to the eNB.

-   -   frequency carrying interested MBMS service    -   information indicating priorities of MBMS and unicast service    -   information indicating whether current MBMS service is received        per frequency    -   sum of data rates of MBMS services the UE is receiving or        intends to receive

The eNB triggers the handover of the UE to an appropriate frequencyusing the above informations such that the UE receives the MBMS service.Form the view point of the cell, the MBMS service may restrict theunicast service. Using a part of the limited radio resource for MBMSservice decreases the radio resource amount for unicast service and thusincreases the probability of cell congestion. If the cell congestionsituation is defined as insufficient QoS for unicast service to thelarge amount of UEs, it is preferred to hand over the control of the UEto other cell from the view point of the eNB.

If it is more important for a UE to receive the MBMS service than theunicast service, it is preferred to release the unicast service bearerrather than perform handover of the UE. According to an embodiment, theUE reports the priorities of the MBMS service and unicast service inorder for the eNB to operate in such a way. By discriminating betweenthe situation of receiving the MBMS service and the situation of justbeing interested in receiving the MBMS service, i.e. by reportingwhether the MBMS service is received per frequency, the eNB is capableof managing radio resource more efficiently.

In an alternative case, it is also possible to consider the start timeof the interested MBMS service in reporting the interested MBMS serviceprovision frequency. That is, the UE may configure the interested MBMSservice provision frequency information as follows.

The UE reports the interested MBMS service frequency only when the MBMSstart time has passed or is passing soon at the time of transitioning tothe connected mode. In this case, since the UE is likely to be or startreceiving the MBMS service on the reported frequency, it is notnecessary to report whether the MBMS service is being received.

In the case that the eNB has released the unicast bearer of the UE whichis receiving the MBMS service due to the cell congestion, it ispreferred for the UE to refrain from attempting recovery of the unicastbearer. In the present invention, when transmitting the control messageinstructing bearer release to the UE, the eNB notifies the UE that thereason for the bearer release is the cell congestion caused by the MBMSservice such that the UE controls the unicast bearer reestablishmentprocedure based on the bearer release reason.

Referring to FIG. 5, the UE initiates an RRC connection setup procedureat step 505. The RRC connection setup procedure is performed in such away that the UE sends the eNB an RRC CONNECTION REQUEST message, the eNBsends the UE an RRC CONNECTION SETUP message, and the UE sends the eNBan RRC CONNECTION SETUP COMPLETE MESSAGE.

The RRC connection setup procedure is initiated with the request forconnection setup from the higher layer of the RRC. The higher layer mayrequest for RRC connection setup for performing Tracking Area update(TAU) or unicast bearer configuration. If the RRC connection setupcompletes, the higher layer sends the MME a TAU message or a bearersetup request message.

The UE transmits the RRC connection setup complete message including theMBMS information at step 510. If the interested MBMS service start timehas passed or arrives immediately, the UE includes the interested MBMSservice providing frequency information in the MBMS information. TheMBMS information includes ‘sum of data rates of MBMS services which theUE is receiving or intending to receive’ which is the informationnecessary for preventing the sum of the unicast service data ratesprovided by the eNB from exceeding the processing capability of the UE.

Once the RRC connection setup has completed, the UE performs normaloperations with the eNB, i.e. receives the unicast service through theestablished bearer, and measurements and handover according to theinstruction of the eNB. As described above, if the service cell of theUE undergoes cell congestion, the eNB may release the unicast servicebearer having the priority lower than that of the MBMS service. At thistime, the eNB may send the UE a control message including an indicatorindicating the bearer to be released. Afterward, the UE receives thecontrol message instructing to release the radio data bearer at step515. This control message may be the RRC CONNECTION RECONFIGURATIONmessage. The radio data bearer release may be resulted from the cellcongestion or normal radio resource management.

The UE determines whether the control message includes the indicator 1at step 520. If the indicator 1 is not included, the procedure goes tostep 525 and, otherwise of the indicator 1 is included, step 530.

The RRC device determines whether the control message includes a fullconfiguration indicator and, if not, transfers the followinginformations to the higher layer at step 525.

-   -   Fact that DRB has released.    -   Identifier of higher layer bearer (Enhanced Packet System (EPS)        bearer) connected to the released DRB)

The full configuration indicator is the indicator indicating that theeNB instructs the UE to perform the following operation.

-   -   Release all currently configured DRBs and reconfigure DRB        according to the configuration information included in the        control message.

The reason for performing the full configuration is because when the UEperforms handover to an earlier release eNB the new eNB may notunderstand the current DRB configuration of the UE.

If the full configuration indicator is included, the UE notifies thehigher layer of the information on the bearer which is not indicated bythe reconfiguration information included in the control message amongthe released bearers. If the reconfiguration information on the releasedbearer is included in the control message, the above information is notdelivered to the higher layer.

If it is detected that the DRB for a certain EPS bearer providing theunicast service has been released, the higher layer may request for EPSbearer reconfiguration according to the user's preference or initiatethe procedure of requesting for release of EPS bearer.

At step 530, the UE attempts reestablishment of the DRB-released EPSbearer only when the following condition is fulfilled.

-   -   Congestion of the current cell is resolved.    -   The priority of unicast service is changed to be higher than        that of MBMS service.

The information on whether the congestion of the current cell has beenresolved is broadcast in a certain SIB. For example, if the Access ClassBaring (ACB, see TS36.331) information of SIB 2 is broadcast, thisindicates that the cell congestion continues and, otherwise if the ACBis not broadcast any more), this indicates that the congestion has beenreleased.

At step 530, the UE may consider the congestion situation of the currentcell and the priorities of the unicast service and MBMS service indetermining whether to establish new EPS bearer afterward. That is, ifthe MBMS service is received with priority, the UE does not initiate theEPS bearer setup request procedure in the congestion situation of thecell.

FIG. 6 is a flowchart illustrating a method for a UE non-interested inreceiving MBMS to adjust the cell reselection priority of a cellproviding MBMS according to an embodiment of the present invention.

It is preferred that the UE which is not interested in the MBMS servicedoes not camp on the cell which is in congested state and provides MBMSservice. According to an embodiment of the present invention, the UEwhich is not interested in receiving MBMS adjusts the cell reselectionpriority of the frequency of the corresponding cell to drop theprobability of camping on the corresponding cell.

Referring to FIG. 6, the UE which is not interested in receiving MBMSinitiates cell reselection procedure at step 650. The cell reselectionprocedure is of comparing the channel qualities of the serving andneighbor cells to determine whether to camp on the neighboring cellfulfilling a predetermine condition. The cell which fulfills apredetermined channel quality condition and is not barring access isfound, the UE camps on the corresponding cell at step 610. Afterward,the UE receives the system information from the new cell to acquire theinformation necessary for communication in the new cell. The UE alsomonitors the paging channel of the new cell.

The UE determines whether the cell is in the congestion state based onthe system information at step 615. For example, if ACB information isbroadcast, this means that the cell is in the congestion state. If it isdetermined that the cell is not in the congested state, the UE maintainsthe cell reselection priority of the current serving frequency withoutadjustment at step 625.

If it is determined that the cell is in the congestion state at step615, the UE determines whether the MBMS-related system information isbroadcast in the cell at step 620. The MBMS-related system informationmay include the information on the channel necessary for receiving theMBMS service, i.e. MBMS Control Channel (MCCH) configurationinformation. It may be any SAI-related information.

If it is determined that the MBMS-related system information isbroadcast at step 620, the UE is aware that the cell provides the MBMSservice in the congestion state. In this case, the UE adjusts the cellreselection priority of the current frequency, i.e. serving frequency,to a predetermined value for a predetermined duration at step 630. Thepredetermined value may be the smallest value. The predeterminedduration may be of long enough, e.g. 300 seconds. By adjusting the cellreselection priority in this way, the UE is capable of dropping theprobability of camping on the cell of the corresponding frequency forthe predetermined duration.

FIG. 7 is a flowchart illustrating a method for the UE which isinterested in receiving MBMS to determine whether to transmit accessnotification message according to an embodiment of the presentinvention.

If the UE as a member of a Closed Subscriber Group (CSG) approaches aCSG cell, it transmits a control message called proximity notificationmessage (Proximity Indication) to the eNB to perform handover to the CSGcell. The control message includes the frequency information of the CSGcell, and the eNB may configure frequency measurement to the UE toinitiate the handover of the UE to the CSG cell.

If the CSG member UE which is receiving or intending to receive the MBMSservice performs handover to the CSG cell, it may not receive the MBMSservice. Accordingly, it is preferred that the UE which gives the higherreception priority to the MBMS service as compared to the unicastservice does not initiate the procedure for handover to the CSG cellalthough it approaches the CSG cell. The UE operation is described withreference to FIG. 7.

The UE realizes its approach to the CSG cell area at step 705. Forexample, the UE memorizes the identifier of the macro cell overlappedwith its CSG cell and, if it enters the macro cell, realizes that it hasapproached the CSG cell area. Also, it is possible to determine itsapproach to the CSG cell area using the RF fingerprint information ofthe CSG cell (channel quality information of neighbor cells).

Afterward, the UE determines whether it is interested in receiving theMBMS service at step 710 and, if not, the procedure goes to step 715and, otherwise, step 720.

At step 715, the UE determines whether the proximity indication isconfigured and, if so, initiates a procedure of moving to its CSG cellat step 723, e.g. generates the proximity indication to the eNB. If noproximity indication is configured, the procedure goes to step 725.

The eNB notifies the UE whether the proximity indication is configured.For example, if the eNB notifies the UE of the configuration ofproximity indication in or after the RRC connection setup procedure,this means that the proximity indication is configured to thecorresponding cell. Unless the eNB notifies the UE of the configurationof proximity indication explicitly, this means that the proximityindication is not configured to the corresponding cell. The reason forthis operation is to prevent the UE from transmitting the proximityindication to the eNB which does not support proximity indicationbecause the proximity indication may be supported or not depending onthe software release of the eNB.

The UE determines whether the MBMS service has priority compared to theunicast service at step 720. Or, the UE determines whether it has beenreported that the MBMS service has priority compared to the unicastservice in the current or later MBMS service reception without report onpriority change since then. If it is determined that the MBMS servicehas priority compared to the unicast service, the procedure goes to step715.

If it is determined that the MBMS service has priority compared to theunicast service, the UE does not move to the CSG cell and the proceduregoes to step 725.

At step 725, the UE suspends the procedure for moving to the CSG celluntil the following condition is fulfilled.

-   -   The UE stays in the CSG cell area, the proximity indication        report is configured, and the priority of the unicast service is        changed to be higher than that of the MBMS service.

In order to increase the data rate of the UE, a carrier aggregation ofaggregating a plurality of serving cells for one UE is introduced. Adescription is made of the carrier aggregation briefly with reference toFIG. 8.

FIG. 8 is a diagram illustrating carrier aggregation.

Referring to FIG. 8, an eNB transmits and receives signals throughmultiple carriers across a plurality of frequency bands. For example,when the eNB 805 transmits signals on the carrier 813 with the downlinkcenter frequency f1 and the carrier 810 with the downlink centerfrequency 815, the UE transmits/receives data using one of the twocarriers in the conventional system. However, the UE having the carrieraggregation capability may transmit/receive data using a plurality ofcarriers simultaneously. The eNB 805 allocates more carriers to the UE830 having the carrier aggregation capability so as to increase the datarate of the UE 830. Aggregating the downlink or uplink carriers fortransmitting or receiving signals is referred to as carrier aggregation.

The terms used frequently in the following description are explainedhereinafter.

Assuming that a cell is configured with one downlink carrier and oneuplink carrier in the conventional concept, the carrier aggregation canbe understood as if the UE communicates data via multiple cells. Withthe use of carrier aggregation, the peak data rate increases inproportion to the number of aggregated carriers.

In the following description, the phrase “the UE receives data through acertain downlink carrier or transmits data through a certain uplinkcarrier” means to transmit or receive data through control and datachannels provided in a cell corresponding to center frequencies andfrequency bands of the downlink and uplink carriers. Particularly in thepresent invention, the carrier aggregation is expressed in such a phraseas “a plurality of serving cells are configured” along with the terms“primary serving cell (PCell),” “secondary serving cell (SCell),” and“activated serving cell.” These terms have the same meanings as used inthe LTE mobile communication system and detailed definitions thereof arespecified in TS 36.331 and TS 36.321. Also, the terms“timeAlignmentTimer,” “Activation/Deactivation MAC Control Element,” and“C-RNTI MAC CE” used in the present invention are specified in TS36.321.

FIG. 9 is a flowchart illustrating a method for the UE configured with aplurality of serving cells to perform random access according to anembodiment of the present invention.

The UE configured with a plurality of serving cells may transmit apreamble in the PCell or a SCell in the random access procedure. Therandom access procedure may be performed for various reasons and, inmost cases, the UE transmits the preamble in the PCell. In predefinedcases (e.g. when the eNB instructs the UE to transmit the preamble in aspecific SCell), however, the UE transmits the preamble in the SCell. Inthe case that the eNB intends to check the uplink transmission timing ina certain SCell, the eNB may instruct the UE to perform the randomaccess procedure.

In an embodiment of the present invention, the UE performs the randomaccess procedure distinctly depending on whether the preamble istransmitted in the PCell or the SCell.

The UE operation is described with reference to FIG. 9.

The UE first acquires random access information at step 900. The randomaccess information may include followings.

-   -   Maximum number of preamble transmissions (preambleTransMax):        Maximum number of preamble transmissions in the random access        operation of the UE before starting a predetermined operation.        The predetermined operation may be the RRC connection        reestablishment. The eNB sets the preambleTransMax to an        appropriate value to prevent the preamble from being transmitted        infinitely.    -   Random access response window size (ra-ResponseWindowSize): The        random access response window is the maximum duration for which        the UE which has transmitted the preamble wait for receiving the        Random Access Response (RAR) message. If no RAR is received        before the expiry of the random access response window, the UE        may retransmit the preamble.

The UE which has not perform handover after RRC connection establishmentin a certain cell is capable of acquiring the random access informationin one of the following two ways.

-   -   Acquiring from the system information    -   Acquiring from a dedicated RRC control message. The dedicated        RRC control message may be the RRC Connection Reconfiguration        message which instructs the SCell configuration but does not        command handover.

In the following description, the random access information acquiredthrough the first method is referred to as random access information 1and the random access information acquired through the second method isreferred to as random access information 2. That is, The UE may have therandom access information as follows at a certain time point.

-   -   First preambleTransMax, First ra-ResponseWindowSize    -   Second preambleTransMax, Second ra-ResponseWindowSize

The first preambleTransMax and the first ra-ResponseWindowSize areacquired from the system information of the PCell, and the secondpreambleTransMax and the second ra-ResponseWindowSize are given througha predetermined dedicated RRC message.

The random access procedure is triggered at step 905. If the data havingthe high priority occurs in the UE or if the eNB instructs to performrandom access, the UE triggers the random access procedure. The UEtransmits the preamble in a predetermined serving cell at step 910 anddetermines whether the serving cell in which it has transmitted thepreamble is the PCell or SCell. If it is the PCell, the procedure goesto step 920 and, otherwise if it is the SCell, step 925.

The UE controls the preamble transmission and retransmission by applyingthe first preambleTransMax and the first ra-ResposneWindowsize at step920 and by applying the second preambleTransMax and the secondra-ResposneWindowsize at step 925.

Controlling the preamble transmission and retransmission process usingthe preambleTransMax and ra-ResponseWindowSize has the meaning asfollows.

The UE monitors to determine whether a valid RAR message is received forthe RAR window after transmitting the preamble. If no valid RAR messageis received before the RAR window expires, the UE increases the transmitpower as much as predetermined amount and retransmits the preamble. Inthe normal case, the eNB receives the preamble transmitted by the UE atany time and transmits the RAR message as reply. However, the channelcondition of the UE may be significantly bad or the eNB cannot transmitthe RAR message to the UE due to preamble congestion to the eNB. In thiscase, if the number of preamble transmissions reaches preambleTransMax,the UE performs a predetermined tapering operation, e.g. stoppingpreamble transmission or reestablishing RRC connection. Controlling thepreamble transmission and retransmission means determining a preambleretransmission timing and whether to retransmit preamble by applyingpreambleTransMax and ra-ResposneWindowSize.

The reason for applying the second random access information when the UEtransmits the preamble in the SCell at step 925 is to make it possiblefor the UE to perform random access without acquiring the systeminformation from the SCell. If the UE has to acquire the systeminformation in the SCell, it has to acquire the system informationbefore starting data communication in the SCell, resulting in delay.

At step 925, the preamble transmission and retransmission process may becontrolled by applying the second preambleTransMax and the firstra-ResponseWindowSize instead of the second preambleTransMax and thesecond ra-ResponseWindowSize.

Afterward, the UE determines whether the random access procedure hascompleted successfully before the number of preamble transmissionsreaches the preambleTransMax at step 930. If the random access procedurehas completed successfully before the number of preamble transmissionreaches the preambleTransMax, the UE ends the procedure at step 935. Ifthe random access procedure has not completed successfully before thenumber of preamble transmission reaches the preambleTransMax, the UEdetermines whether the preamble has been transmitted in the PCell orSCell at step 940. If the preamble has been transmitted in the PCell,the UE initiates the RRC connection reestablishment at step 945. If thepreamble has been transmitted in the SCell, the UE stops preambletransmission at step 950.

If the preamble has been transmitted in the SCell, the preambleTransMaxis determined by applying the preambleTransMax parameter signaled to thecorresponding cell while the RAR window size is determined as the valuedefined for the PCell, i.e. the value broadcast through the systeminformation of the PCell. This is because although it is preferred todetermine the preambleTransMax by applying the state of the cell inwhich the preamble is transmitted, i.e. although the difference of thevalue may be great depending on the cell in which the preamble istransmitted, the RAR window size, as the parameter for defining theduration for the UE to try receiving the RAR, has no large differencebetween the cells.

The UE controls the preamble transmission and RAR reception operationsby applying the selected parameters and, if it fails to receive RAR eventhough the preamble has transmitted as many as preambleTransMax or ifthe random access procedure has not completed successfully, performs anecessary follow-up operation. The follow-up operation is also defineddifferently depending on the cell in which the UE has transmitted thepreamble. If the preamble has been transmitted in the PCell and if therandom access fails before the number of preamble transmission reachesthe preambleTransMax, the UE determines that there is significantconnection problem with the current PCell and initiates the RRCconnection reestablishment procedure at step 945. The RRC connectionreestablishment procedure is specified in 36.331 in detail.

If the preamble has been transmitted and if the random access failsbefore the number of preamble transmissions reaches thepreambleTransMax, the UE determines that there is significant connectionproblem with the SCell and stops preamble transmission at step 950. Inthis case the UE does not perform the RRC connection reestablishmentprocedure because it has no connection problem in the PCell althoughthere is a connection problem with the SCell. For reference, if there isa connection problem with the PCell, the normal communication isimpossible in spite of no connection problem with the SCell but, in theopposite case, it is possible to continue communication through thePCell.

FIG. 10 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

Referring to FIG. 10, the UE according to an embodiment of the presentinvention includes a transceiver 1005, a controller 1010, amultiplexer/demultiplexer 1015, a control message processor/RRCcontroller 1030, and higher layer processors 1020 and 1025.

The transceiver 1005 receives data including MBMS and control signalsthrough the downlink channel of a serving cell and transmits data andcontrol signals through the uplink channel. In the case that a pluralityof serving cells are configured, the transceiver 1005 transmits/receivesdata and control signals through a plurality serving cells.

The multiplexer/demultiplexer 1015 multiplexes the data generated by thehigher layer processors 1020 and 1025 and the control message processor1030 and demultiplexes the data received by the transceiver 1005 todeliver the demultiplexed signal to the higher layer processors 1020 and1025 and the control message processor 1030.

The control message processor 1030 is an RRC layer device and processesthe control message received from the eNB to take a necessary action.For example, if the system information is received from the eNB, thecontrol message processor 1030 transfers the related information to thecontroller. It transfers the cell reselection priority informationreceived from the eNB to the controller.

The higher layer processors 1020 and 1025 may be implemented perservice. The higher layer processor processes the data generated by theuser service such as File Transfer Protocol (FTP) and Voice overInternet Protocol (VoIP) and transfers the processed data to themultiplexer/demultiplexer 1015 and processes the data from themultiplexer/demultiplexer 1015 and transfers the processed data to theservice applications of the higher layer. The higher layer processor mayinclude RLC layer device, PDCP layer device, and IP layer device.

The control unit 1010 checks the scheduling command, e.g. uplink grants,received by the transceiver 1005 and controls the transceiver 1005 andmultiplexer/demultiplexer 1015 to perform uplink transmission withappropriate transmission resource at appropriate time. The controllermay perform the operations proposed in FIGS. 4, 5, 6, 7, and 9. That is,the controller may adjusts the cell reselection priority appropriatelyand control the bearer reconfiguration procedure and random accessprocedure.

FIG. 11 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

Referring to FIG. 11, the eNB includes a transceiver 1105, a controller1110, a multiplexer/demultiplexer 1120, a control message processor/RRCcontroller 1135, higher layer processors 1125 and 1130, and a scheduler1115.

The transceiver 1105 transmits data and control signals on the downlinkcarriers and receives data and control signals on the uplink carriers.In the case that a plurality of carriers are configured, the transceiver1105 transmits and receives data and control signals on the multiplecarriers.

The multiplexer/demultiplexer 1120 multiplexes the data generated by thehigher layer processors 1125 and 1130 and the control message processor1135 and demultiplexes the data received by the transceiver 1105 anddelivers the demultiplexed data to appropriate higher layer processors1125 and 1130, the control message processor 1135, and the controller1110. The control message processor 1135 processes the control messagetransmitted by the UE to take a necessary operation and generates thecontrol message to be transmitted to the UE to the low layers.

The higher layer processor 1125 and 1130 may be implemented per bearerprocesses the data to be transferred to the SGW or another eNB into RLCPDUs and transfers the RLC PDUs to the multiplexer/demultiplexer 1120 orprocesses the RLC PDUs from the multiplexer/demultiplexer 1120 togenerate PDCP SDUs to the SGW or another eNB.

The scheduler allocates transmission resource to the UE at anappropriate time in consideration of the buffer state and channel stateof the UE and controls the transceiver to process the signal to betransmitted to the UE and received from the UE.

The controller may perform the control operations concerning the eNBoperations proposed in FIGS. 4, 5, 6, 7, and 9. For example, the controlunit configures the cell reselection priority to the UE and whether totransmit proximity indication and controls the operation of transmittingRAR message to the UE in the RAR window.

Although preferred embodiments of the invention have been describedusing specific terms, the specification and drawings are to be regardedin an illustrative rather than a restrictive sense in order to helpunderstand the present invention. It is obvious to those skilled in theart that various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the invention.

What is claimed is:
 1. A method for a random access of a secondary cellin a mobile communication system using Carrier Aggregation (CA), themethod comprising: receiving, by a terminal, a Random Access Response(RAR) window size indicating duration of a random access response windowfor receiving a random access response on a primary cell via systeminformation; receiving, by the terminal, a maximum number of preambletransmission values for the random access of the secondary cell on aprimary cell via dedicated control information; transmitting, by theterminal, a random access preamble for the random access of thesecondary cell; and monitoring, by the terminal, a RAR based on the RARwindow size.
 2. The method of the claim 1, wherein the transmitting therandom access preamble is based on the maximum number of preambletransmission values.
 3. The method of the claim 1, wherein thetransmitting the random access preamble further comprises: increasing apreamble transmission counter by one.
 4. The method of the claim 1,wherein the transmitting the random access preamble further comprises:increasing a preamble transmission counter by one if the random accessresponse is not received within the random access response window. 5.The method of claim 4, wherein the method further comprising: stoppingthe random access of the secondary cell if the preamble transmissioncounter is greater than the maximum number of preamble transmissionvalues.
 6. A terminal for a random access of a secondary cell in amobile communication system using Carrier Aggregation (CA), the terminalcomprising: a transceiver configured to transmit and receive a signal;and a controller configured to receive a Random Access Response (RAR)window size indicating duration of a random access response window forreceiving a random access response on a primary cell via systeminformation, to receive a maximum number of preamble transmission valuesfor the random access of the secondary cell on a primary cell viadedicated control information, to transmit a random access preamble forthe random access of the secondary cell, and to monitor a RAR based onthe RAR window size.
 7. The terminal of the claim 6, wherein thecontroller is configured to transmit the random access preamble based onthe maximum number of preamble transmission values.
 8. The terminal ofthe claim 6, wherein the controller is configured to increase a preambletransmission counter by one.
 9. The terminal of the claim 6, wherein thecontroller configured to increase a preamble transmission counter by oneif the random access response is not received within the random accessresponse window.
 10. The terminal of claim 9, wherein the controller isconfigured to stop the random access of the secondary cell if thepreamble transmission counter is greater than the maximum number ofpreamble transmission values.
 11. A base station for a random access ofa secondary cell in a mobile communication system using CarrierAggregation (CA), the base station comprising: a transceiver configuredto transmit and receive a signal; and a controller configured totransmit a Random Access Response (RAR) window size indicating durationof a random access response window for a terminal to receive a randomaccess response on a primary cell via system information, to transmit amaximum number of preamble transmission values for the random access ofthe secondary cell on a primary cell via dedicated control information,and to receive a random access preamble for the random access of thesecondary cell.
 12. The base station of the claim 11, wherein the randomaccess preamble is transmitted based on the maximum number of preambletransmission values, by the terminal.
 13. The base station of the claim11, wherein a preamble transmission counter is increased by one.
 14. Thebase station of the claim 11, wherein a preamble transmission counter isincreased by one if the random access response is not received withinthe random access response window by the terminal.
 15. The base stationof claim 14, wherein the random access of the secondary cell is stoppedif the preamble transmission counter is greater than the maximum numberof preamble transmission values.